Automotive refinishers typically maintain a relatively small inventory of paint colors which can be mixed selectively according to preset recipes to achieve a precise color match for virtually any make and model year of automobile. Thus, the automotive refinisher can realize considerable inventory cost savings by maintaining a relatively small inventory of paint colors which can be mixed, when needed, on a batch-wise basis in order to match a particular original paint color. Indeed, it would essentially be cost-prohibitive for automotive refinishers to maintain an entire inventory of premixed paint colors matching the original paint for all automobile manufacturers since the formulations of automotive paint colors can, and often do, change from one model year to the next.
The conventional practice, however, in the automotive refinishing business is for the individual paint colors to be admixed manually. That is, when a specific paint color for a particular automobile make and model year is needed to be matched, the automotive refinisher will manually dispense each individual paint color component from the refinisher's inventory until the desired dosage weight (which is determined by a color-matching recipe) is achieved. Therefore, by combining these manually dispensed dosage weights for each individual paint color component, a batch of the desired automotive paint color to be matched may be obtained.
However, manually dispensing individual paint color components cannot always accurately duplicate the paint formulation recipes. For example, there exists the practical limit of scale accuracy when the individual doses of paint components are weighed. Furthermore, the weighed doses of individual paint components are typically dispensed sequentially into a single mixing receptacle so as to minimize inaccuracies that might otherwise accrue by dispensing the individual doses into segregated weighing receptacles and thereafter combining the individual doses. Thus, there exists the real possibility that human error could cause a single paint color to be over-dispensed into a batch of previously dispensed paint color components resulting in the waste of the entire paint batch.
Automated dosing equipment is known and employed in a number of end-use applications where highly precise quantities (doses) of components are desired to be admixed according to preset recipes. For example, some commercial paint mixing systems are known which are provided with a scale and a computer-assisted correction function. According to such known systems, when an over-dose of a particular component occurs, the other component(s) will be added in small quantities under computer control so as to compensate for the over-dosed component. However, the addition of additional quantities of components to compensate for the over-dosed component could its,elf lead to new dosing errors and is therefore not an entirely satisfactory solution.
An automated dosing apparatus is also known from published European Patent Application No. 0353197 (hereinafter "EP'197") whereby individual flowable components may be added together and mixed in precise quantities. Specifically, FIG. 2 in EP '197 discloses a system which includes a multiple outlet (e.g., 3-way) diverting valve whereby an individual component flowing from a pressurized supply container may either be directed to a dosing head or recirculated to its supply canister. However, since the supply canister is pressurized, a downstream pump is necessary in order to overcome the pressure in the supply canister during recirculation and thereby cause the individual component to return to the supply canister through the recirculation line.
While one could envision using automated dosing equipment of the variety disclosed in EP '197 for purposes of dispensing highly accurate doses of individual automotive paint colors (and thereby render obsolete the conventional manual dosing techniques used by automotive refinishers), there would still be present several real, non-trivial technical problems. For example, since automotive refinish paint is typically a mixture of solid pigments in a suitable carrier (e.g., resin and solvent), there exists the possibility of pigment sedimentation and/or carrier flotation (hereinafter more simply termed "paint separation") in the dosing equipment, particularly in the lines which feed paint to the dispensing head from a paint supply container, during those time periods that the equipment is idle. Paint separation could therefore result in gross inaccuracies during the automated dosing procedure leading to color variations, and hence color mismatches.
The recirculation of the paint through the automated dosing equipment as part of the equipment start-up procedures and/or prior to each dosing operation could remedy paint separation problems. However, as noted briefly above, in the pressurized paint supply system disclosed in EP '197, the paint would only recirculate through the diverting valve and not through the dosing head (i.e., since the diverting valve is positioned upstream of the dosing head). Thus, any paint which lies dormant in the line fluid-connecting the diverting valve to the dosing head would still be subject to paint separation.
It would therefore be highly desirable in automotive refinish paint applications if a recirculation system and technique could be provided for automated dosing apparatus which allows individual paint components to be recirculated through the dosing head. Such a recirculation system could thus ensure that no pigment sedimentation exists in the individual paint component dose and thereby increase the accuracy associated with the automated batch mixture of paint components. It is towards providing such improvements that the present invention is directed.
Broadly, the present invention is embodied in a recirculation system associated with an automated dosing apparatus which employs pressurized supply canisters for the individual flowable components to be dosed and a recirculation loop which permits the flowable components to be recirculated through the dosing head and returned to their respective pressurized supply canisters. The recirculation system according to this invention more specifically includes buffer reservoirs which are fluid-connected to both the dosing head and a respective pressurized supply canister. During a recirculation mode, therefore, a flowable component supplied to the dosing head will be caused to recirculate through channels defined in the dosing head and thereafter be directed to a respective buffer reservoir. The recirculated paint will accumulate in the buffer reservoir until the recirculation mode has been completed. At that time, a transfer mode will be initiated so as to cause the buffer reservoir to be pressurized greater than the pressure existing in the stock canister. This greater pressure within the buffer reservoir will thereby serve to forcibly transfer the accumulated recirculated paint therein to the supply canister.
Any number of such recirculation/flow loops may be provided in the automated apparatus of this invention in dependence upon the number of individual components of flowable material that may need to be admixed in metered amounts.
As a result of this invention, therefore, the flowable components will be completely circulated through the dosing head so as to purge the flow lines to the dispensing nozzle in the dosing head and ensure highly accurate dosing. This advantage of the present invention, as well as others, will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiment.